Development apparatus, image forming apparatus and developing method that employ a magnetic brush

Abstract

In a development apparatus of the hybrid method using a component developer, a development apparatus and a development method are provided that prevent the reduction of density or the occurrence of residual images (ghost images) and can carry out good image forming over a long period of time. A development apparatus has the feature that the surfaces of the toner supporting member and the developer supporting member move in a mutually opposite direction at the part where they are opposite to each others. The development apparatus further employs an electric field in the closest part applied in a direction to recover the toner from the toner supporting member to the developing supporting member, wherein the magnitude of the electric field is in the range from 2.5×10 6 V/m to 5×10 6 V/m. The developer of the development apparatus is such that its share (PD) in the space of the closest part of the opposing portion satisfies the following relationship: 0.09≦PD≦650×Dss.

1. A development apparatus, comprising:
 a developer supporting member which supports developer containing toner and magnetic carrier on a surface of the developer supporting member to convey the developer, wherein the developer supporting member comprises a rotatable sleeve in which a magnet body is fixedly arranged; 
 a toner supporting member which is disposed facing the developer supporting member to receive the toner transferred from the developer supporting member onto a surface of the toner supporting member, to convey the toner to a development area, wherein the developer forms a magnetic brush on the developer supporting member so as to rub the toner supporting member, the toner having passed through the development area is collected onto the developer supporting member by the developer rubbing the toner supporting member, and the surface of the toner supporting member travels in a direction opposite a traveling direction of the surface of the developer supporting member at an opposing portion between the toner supporting member and the developer supporting member; and 
 an electric field forming mechanism which is adapted to form an alternating electric field between the developer supporting member and the toner supporting member, wherein a strength of an electric field in a direction in which the toner is collected from the toner supporting member onto the developer supporting member is in a range from 2.5×10 6  V/m to 5×10 6  V/m at a closest portion between the developer supporting member and the toner supporting member, and a packing density PD of the developer in a space at the closest portion between the developer supporting member and the toner supporting member satisfies the following relationship,
   0.09 ≦PD≦ 650 ×Dss  wherein, 
     PD=M /(ρ× Dss ); 
 
 M (g/m 2 ) is an amount of the developer on the developer supporting member; 
 Dss (m) is a smallest spacial distance between the developer supporting member and the toner supporting member; 
 ρ (g/m 3 ) is a density of the developer, ρ satisfying the equation
   ρ=ρ t×TC+ρc ×(1 −TC ); 
 
 ρt (g/m 3 ) is a density of the toner; 
 ρc (g/m 3 ) is a density of the carrier; and 
 TC is a mass ratio of the toner in the developer. 
 
   
   
     2. The development apparatus of  claim 1 , wherein a strength of an electric field in a direction in which the toner is supplied from the developer supporting member onto the toner supporting member is in a range from 2.5×10 6  V/m to 6×10 6  V/m at the closest portion between the developer supporting member and the toner supporting member. 
   
   
     3. The development apparatus of  claim 1 , wherein the developer contains opposite polarity particles which are different from the toner and the carrier and are charged in an opposite polarity to a polarity of electrostatic charge of the toner. 
   
   
     4. The development apparatus of  claim 3 , wherein a strength of an electric field in a direction in which the toner is supplied from the developer supporting member onto the toner supporting member is in a range from 2.5×10 6  V/m to 6×10 6  V/m at the closest portion between the developer supporting member and the toner supporting member. 
   
   
     5. The development apparatus of  claim 3 , wherein a number average particle diameter of the toner is from 3 to 15 μm, and a number average particle diameter of the opposite polarity particles is from 100 to 1000 nm. 
   
   
     6. An image forming apparatus, comprising:
 an image carrier; 
 an electrostatic latent image forming mechanism which is adapted to form an electrostatic latent image on the image carrier; 
 a development apparatus which is adapted to develop the electrostatic latent image on the image carrier to form a toner image, the development apparatus including:
 a developer supporting member which supports developer containing toner and magnetic carrier on a surface of the developer supporting member to convey the developer; 
 a toner supporting member which is disposed facing the developer supporting member to receive the toner transferred from the developer supporting member onto a surface of the toner supporting member, to convey the toner to a development area, wherein the developer supporting member including a magnet body therein, the developer forms a magnetic brush on the developer supporting member so as to rub the toner supporting member, the toner having passed through the development area is collected onto the developer support member by the developer rubbing the toner supporting member, and the surface of the toner supporting member travels in a direction opposite of a traveling direction of the surface of the developer supporting member at an opposing portion between the toner supporting member and the developer supporting member; 
 
 an electric field forming mechanism which is adapted to form an alternating electric field between the developer supporting member and the toner supporting member, wherein a strength of an electric field in a direction in which the toner is collected from the toner supporting member onto the developer supporting member is in a range from 2.5×10 6  V/m to 5×10 6  V/m at a closest portion between the developer supporting member and the toner supporting member, and 
 an image transfer mechanism which is adapted to transfer the toner image formed on the image carrier onto a recording medium; 
 wherein a packing density PD of the developer in a space at the closest portion between the developer supporting member and the toner supporting member satisfies the following relationship,
   0.09 ≦PD≦ 650 ×Dss  wherein, 
     PD=M /(ρ× Dss ); 
 
 M (g/m 2 ) is an amount of the developer on the developer supporting member; 
 Dss (m) is a smallest spacial distance between the developer supporting member and the toner supporting member; 
 ρ (g/m 3 ) is a density of the developer, ρ satisfying the equation
   ρ=ρ t×TC+ρc ×(1 −TC ); 
 
 ρt (g/m 3 ) is a density of the toner; 
 ρc (g/m 3 ) is a density of the carrier; and 
 TC is a mass ratio of the toner in the developer. 
 
   
   
     7. A developing method, comprising:
 causing a developer supporting member to support developer containing toner and magnetic carrier, the developer supporting member including a magnet body therein; 
 causing a surface of a toner supporting member, which is disposed facing the developer supporting member, to travel in a direction opposite to a traveling direction of a surface of the developer supporting member at an opposing portion between the toner supporting member and the developer supporting member, wherein the developer forms a magnetic brush on the developer supporting member so as to rub the toner supporting member; 
 forming an alternating electric field between the developer supporting member and the toner supporting member so that the strength of the electric field in a direction in which the toner is collected from the toner supporting member onto the developer supporting member by the developer rubbing the toner supporting member is in a range from 2.5×10 6  V/m to 5×10 6  V/m at a closest portion between the developer supporting member and the toner supporting member, and 
 setting a packing density PD of the developer in a space at the closest portion between the developer supporting member and the toner supporting member so as to satisfy the following relationship,
   0.09 ≦PD≦ 650 ×Dss  wherein, 
     PD=M /(ρ× Dss ); 
 
 M (g/m 2 ) is an amount of the developer on the developer supporting member; 
 Dss (m) is a smallest spacial distance between the developer supporting member and the toner supporting member; 
 ρ (g/m 3 ) is a density of the developer, ρ satisfying the equation
   ρ×ρ t×TC+ρc ×(1 −TC ); 
 
 ρt (g/m 3 ) is a density of the toner; 
 ρc (g/m 3 ) is a density of the carrier; and 
 TC is a mass ratio of the toner in the developer. 
 
   
   
     8. The developing method of  claim 7 , wherein the alternating electric field is formed so that a strength of an electric field in a direction in which the toner is supplied from the developer supporting member onto the toner supporting member is in a range from 2.5×10 6  V/m to 6×10 6  V/m at the closest portion between the developer supporting member and the toner supporting member. 
   
   
     9. The developing method of  claim 7 , wherein the developer contains opposite polarity particles which are different from the toner and the carrier and are charged in an opposite polarity to a polarity of electrostatic charge of the toner. 
   
   
     10. The developing method of  claim 9 , wherein the alternating electric field is formed so that a strength of an electric field in a direction in which the toner is supplied from the developer supporting member onto the toner supporting member is in a range from 2.5×10 6  V/m to 6×10 6  V/m at the closest portion between the developer supporting member and the toner supporting member.